The present disclosure relates to a magnetic single-component developer.
Image forming methods, such as an electrophotographic method and the like, generally include charging the surface of an electrostatic latent image bearing member (photoconductor) by corona discharging or the like, and then forming electrostatic latent images by exposing the charged electrostatic latent image bearing member with a laser or the like. The electrostatic latent images are developed with toners to form toner images, and the toner images are further transferred to recording media to form high-quality images. The toners used for forming the toner images are generally produced by mixing a binder resin such as a thermoplastic resin with a colorant, a charge control agent, a release agent, etc., and kneading, pulverizing, and classifying the resultant mixture to produce toner particles having an average particle diameter of 5 to 10 μm.
Further, so as to impart fluidity to the toners, suppress a charging defect of the toners, and improve the cleaning properties of the toners remaining untransfered on a photoconductor, the toners are spheroidized, and an external additive such as a silica and an inorganic fine powder such as titanium oxide is added to the toners.
At present, known dry development methods in various electrostatic copying systems, which are put to practical use, include a two-component development system using a toner and a carrier such as an iron powder, and a magnetic single-component development system using a toner containing a magnetic powder therein without using a carrier.
With respect to the toners used for the magnetic single-component development system, there are known magnetic toners described below which are intended to improve the fluidity of toners and charge toners. Examples of the known toners include a magnetic toner which is surface-treated by heat treatment and has a dielectric loss of 3.5×10−3 or less, and a magnetic toner containing toner particles spheroidized by heat treatment.
However, the magnetic toners may cause bleed out of the release agent contained in the toners to the toner surfaces due to heating in the toner production process, heat generated by friction, or the like. When the toner containing the release agent bled out to the toner surfaces is used, during long-term printing, the toner is stirred in a development apparatus for a long time to cause deterioration in fluidity of the toner or difficulty in charging the toner to a desired charge amount. When the toner is not charged to the desired charge amount, there is difficulty in forming an image with a desired image density.
In addition, in fixing an image using a heat-transfer member, such as a fixing roller or the like, the heat-transfer member may be charged with electricity by contact with a toner image. It is known that when the heat-transfer member is charged, electric charges electrostatically repel or attract an unfixed toner image to cause an image defect that is referred to as “ scattered character ” (phenomenon that toner scatters and adheres near a character or the like in a fixed image). The image defect of “scattered character” easily occurs when the toner is not charged to a desired charge amount.
In order to resolve the problem with the charge amounts of the above-described magnetic toners, it is considered to decrease the amount of release agent used or not to use the release agent. However, when the amount of the release agent used is decreased or when the release agent is not used, offset easily occurs due to fusion of the toner to a heated fixing roller.